Denver boasts one of the country’s fastest-growing economies and expects to add tens of thousands of new residents by the end of the decade.

The city’s rapid and continued expansion comes at a cost, though. Air quality on the Front Range languishes, pollution threatens the city’s most vulnerable populations and experts worry for the region’s water supply.

Whoever voters elect to run Denver and to sit on its council can take action most directly, experts say, by relying on new technology, tweaking building and zoning codes, partnering with nearby governments and state lawmakers and even limiting the types of lawn care equipment residents can use.

Already Denver officials set a goal to cut greenhouse-gas emissions 65% by 2030 and by 100% over the next decade. The city’s goal is also to hit net-zero energy use by 2040.

Perhaps the biggest piece of Denver’s air-quality problem would be solved by expanding the city’s public transit options, Jill Locantore, executive director of Denver Streets Partnership, said.

Each piece overlaps with the others, Locantore, whose nonprofit works to reduce the city’s dependence on cars, said.

“The key is land use and transportation. Reduce vehicle miles traveled. Reduce land consumption. Reduce water consumption,” Locantore said. “We’ve known the answers for decades, it’s just a matter of political will for implementing them.”

Air quality on the Front Range is so poor that the Environmental Protection Agency reclassified Denver and the rest of the region as “severe” violators of federal standards. As a result gas prices will increase and the number of businesses needing air pollution permits will more than double.

Statewide, transportation accounts for a quarter of carbon emissions, according to a report from the environmental nonprofit Conservation Colorado.

The next mayor will have broad authority to set Denver’s direction for the city’s roads and public transit, Locantore said. As the city is currently laid out, residents are forced to rely on their cars. Often many can’t rely on existing public transit from the cash-strapped Regional Transportation District.

Denver’s mayor could buy additional, dedicated service from RTD, like Boulder does, Danny Katz, executive director of the nonprofit Colorado Public Interest Research Group.

Building new train lines would be expensive, time-consuming and would consume land that’s already occupied or needed for other things, Katz said. Better to increase service on existing train lines to start.

“First run a bunch of buses, build up the ridership and if it becomes clear that, for some reason, a train would run it better then we could do that,” Katz said.

Additional routes plus more consistent service would equal more riders, Katz said. All of that would translate to fewer cars on the road and less carbon emissions.

For the most part, Denver has total control over its own streets, Locantore said. So city officials could transform them to be more bus-friendly. This means the next mayor could also prevent widening roadways to accommodate more vehicles in favor of public transit. Or in the case of shared roadways, the mayor could negotiate with neighboring governments to that same end.

As for cars that can’t be eliminated from the city’s streets, like the thousands of vehicles that Denver owns, Katz said the next mayor could work to phase out gas-powered vehicles in favor of electric ones.

Not only would that shift reduce emissions from thousands of vehicles but it also means the city would likely have to install charging stations around Denver, which could be used by residents also switching to electric vehicles.

“This is so under the control of the mayor,” Locantore said.

Xcel Energy, Colorado’s largest electric utility, has publicly supported efforts to introduce more electric cars to the state. The utility also committed millions of dollars for new charging stations and to convert government and business fleets to electric vehicles.

Others, however, argue against a war on cars in Denver. Tim Jackson, CEO of Colorado Automobile Dealers Association, wrote in a 2020 op-ed that cars are increasingly efficient and that clogging the city’s streets with buses and bikes merely creates more congestion and, therefore, pollution.

“Behind the wheel of every car is a person who has decided that this is the best — sometimes only — way to get where they need to go: work, school, the store, the outdoors,” Jackson wrote.

That’s a big part of the problem, Locantore said. The way Denver is laid out forces people into cars rather than offering them a variety of options.

Increasing the city’s density would mean more people live within walking distance of public transit and other amenities, Locantore said. The City Council holds sway over zoning and building codes and it could change the codes to encourage higher-density, multi-use projects and turn away others that don’t meet the criteria.

The City Council is already working to cut emissions from Denver’s large commercial and multi-family buildings. New building codes approved in January will phase out gas furnaces and water heaters in new construction.

The new mayor must enforce those changes, Katz said. But they could also double down to ensure the city continues to shift away from fossil fuels, further cutting emissions.

The last step of that process, outgoing City Councilman Jolon Clark said, would likely be replacing gas furnaces and water heaters in existing buildings, particularly homes.

Opponents of electrification, like Colorado’s conservative nonprofit, the Common Sense Institute, argue that these types of green building code initiatives could cost billions and question whether the state’s electrical grid can handle the increased demand.

But Clark has repeatedly said that the difference in cost for new construction is minimal and that local, state and federal rebates can help diffuse extra costs for older buildings whenever that time comes.

Energy producers, like Xcel Energy, say they’re prepared to handle the extra demand, the Denver Gazette reported.

In addition the emissions data is unambiguous: Denver’s approximately 17,000 commercial and multi-family buildings pump out nearly half of the city’s greenhouse gas emissions, making them a large target for those looking to improve the region’s air quality.

Another substantial challenge for any environmentally conscious mayor would be one of the Front Range’s biggest and most prominent polluters, which doesn’t actually sit in Denver. The Suncor Energy refinery in Commerce City puts out about 100,000 barrels of oil per day and produces about 40% of the gasoline used in the state, when operating at full capacity.

The refinery has repeatedly violated pollution regulations and a year-long monitoring project recently found that the facility emits more pollutants than previously understood.

Like other emissions and greenhouse gasses, Suncor’s pollution hovers over the entire region, particularly Denver’s Globeville, Elyria and Swansea neighborhoods, Olga Gonzalez, executive director of Cultivando, an environmental and social-justice nonprofit in the area.

Cultivando is also responsible for the most recent report focused on Suncor, which it paid for with money the energy company handed over in a 2020 settlement.

Denver’s next mayor and City Council members might not have direct influence over the refinery, Gonzalez said. But they can lobby state regulators to tighten their grip over the refinery.

“They need to advocate for air quality regulations that actually take human health into account,” Gonzalez said. “These regulations need to be updated to reflect cumulative impacts to human health over a period of decades.”

What’s clear, Locantore said, is that both Denver’s next mayor and its City Council will have broad authority over the city’s direction in the coming years. They have a chance to improve the region’s air quality, cut pollution and conserve water, among other things. The question remaining is whether they’ll have the political will to take action.